The present invention relates to the field of radio receivers in general, including radio receivers used in wireless telecommunications/mobile phones, and more particularly to controlling the linearity of a radio receiver.
Power consumption is an essential performance parameter of a radio receiver and in particular of all portable (battery-powered) radio receivers. There are several common radio systems that have strict limitations on power consumption, such as the limitations imposed for cellular communications (GSM, IS-95, AMPS, etc.), for cordless phones (DECT), and for wireless connectivity systems (WLAN, Bluetooth). All such systems benefit from being able to operate at low power, since operating at lower power provides a larger margin for meeting any imposed limitation on power consumption. In particular, so-called third generation mobile phones, expected to become available in the near future, will consume significantly more power than current generation mobile phones because of the many additional services the third-generation mobiles will provide. Power is consumed by the transceiver of a mobile phone in both transmitting and receiving wireless signals. In receiving a radio signal at a particular frequency, the radio receiver portion of a transceiver can be made to act more or less linearly in that it can be made to tolerate more or less of all signals not transmitted at the desired frequency. The more linearly a radio receiver is made to operate, the more power it consumes (because to operate more linearly, more power must be provided to active components of a receiver to tolerate unwanted signal).
One particular problem that is managed by controlling the linearity of a receiver is intermodulation distortion, referring to the so-called third-order intermodulation distortion power (PIMD3) aliasing onto the frequency (channel) to which the receiver is tuned. In an environment with significant intermodulation distortion, a receiver must be made to act more linearly so as to avoid receiving unwanted signals. However, when signal conditions change so that intermodulation distortion is insignificant, then a receiver can be allowed to operate less linearly, and so use less power. Thus, what is needed for use with a receiver is a detector of potential intermodulation distortion (intermodulation distortion that is to be avoided by adjusting the linearity requirement for the receiver), a detector that provides one or more indicators of the potential intermodulation distortion and so provides information useful to the receiver in establishing a linearity requirement for operation of the receiver.
Although a detector of potential intermodulation distortion is particularly useful in reducing power consumption, such a device can be used to measure intermodulation performance distortion for other purposes as well, such as characterizing a radio network with respect to intermodulation distortion which is useful in the design of the radio network. In such an application, an intermodulation detector can be operated as a standalone measurement device, not connected to a receiver operating in a radio system. (In such an application, the measurement set up need not necessarily be power limited.) Other applications for an intermodulation detector are also possible.
Thus, what is needed more generally is a detector of potential intermodulation distortion, whether or not the detector is provided as part of a receiver system (including a radio receiver for use with some radio network). Such a detector should be able to be implemented using either analog or digital signal processing techniques, depending on the particular application and available implementation technologies.
Accordingly, in a first aspect of the invention a method is provided including: a step, responsive to a received signal over a predetermined wide bandwidth and responsive to a tuner signal at a predetermined tuner frequency, of providing a selected signal at a selected signal frequency; and a step of processing the selected signal so as to provide a detector signal indicating intermodulation distortion power at the selected signal frequency.
In accord with the first aspect of the invention, the method may also include a step of adjusting a linearity requirement for a receiver module based on the signal indicating the intermodulation distortion power, and the step of processing the mixed signal may be performed using a detector circuit that is substantially more responsive to intermodulation interference than the receiver module.
Also in accord with the first aspect of the invention, the step of measuring intermodulation distortion power may include: a step of squaring the selected signal; an optional step of providing the squared signal in a suitable digital form; a step of multiplying the squared signal by the baseband signal to provide a cubed signal; and a step of providing the cubed signal in a suitable digital form.
In a second aspect of the invention, an apparatus is provided, including: means, responsive to a received signal over a predetermined wide bandwidth and responsive to a tuner signal at a predetermined tuner frequency, for providing a selected signal at a selected signal frequency; and means for processing the selected signal so as to provide a detector signal indicating intermodulation distortion power at the selected signal frequency.
In accord with the second aspect of the invention, the apparatus may also include means for adjusting a linearity requirement for a receiver module based on the signal indicating the intermodulation distortion power (PIMD3), and the means for processing the mixed signal may be performed using a detector circuit that is substantially more responsive to intermodulation interference than the receiver module.
Also in accord with the second aspect of the invention, the means for processing the selected signal may include: means for squaring a signal derived from the selected signal, and so providing a squared signal; means for multiplying the squared signal with the selected signal, and so providing a cubed signal; and means for processing the cubed signal so as to provide the detector signal indicating intermodulation distortion power.
Also in accord with the second aspect of the invention, the means for providing a selected signal at a selected signal frequency may include means for providing a baseband signal, and further, all operations including those performed by the means for providing a baseband signal may be performed after analog-to-digital conversion.
Still also in accord with the second aspect of the invention, the apparatus may also include an analog-to-digital conversion means for performing an analog-to-digital conversion that is disposed at some node of the apparatus so that at least some of the signal processing performed by the apparatus is digital signal processing performed after the analog-to-digital conversion means.
In a third aspect of the invention, a radio transceiver is provided including a radio receiver that includes an apparatus according to the second aspect of the invention.
The invention is of use in both a standalone mode, where it can be used to characterize a radio environment over some bandwidth, independent of any particular receiver, which might be done for example in order to optimize the performance of a radio network, but could also be done independent of any particular radio network. Although the prior art teaches various equipment for performing such measurements, it is desirable to study the radio environment of a radio network using different measurement techniques. The invention provides measurements using a simple and inexpensive device and makes it possible to collect a larger amount of data for use in adjusting the operation of a radio network.
It is also useful as a part of a system providing information about the radio environment in which the system operates; for example, it can provide radio environment measurement information (and in particular the third-order intermodulation distortion power PIMD3) useful to a radio receiver system, including a radio receiver module, in adjusting the linearity of the radio receiver module.